Phenotypic Variability in Novel Doublecortin Gene Variants Associated with Subcortical Band Heterotopia.

Doublecortin, encoded by the DCX gene, plays a crucial role in the neuronal migration process during brain development. Pathogenic variants of the DCX gene are the major causes of the "lissencephaly (LIS) spectrum", which comprehends a milder phenotype like Subcortical Band Heterotopia (SBH) in heterozygous female subjects. We performed targeted sequencing in three unrelated female cases with SBH. We identified three DCX-related variants: a novel missense (c.601A>G: p.Lys201Glu), a novel nonsense (c.210C>G: p.Tyr70*), and a previously identified nonsense (c.907C>T: p.Arg303*) variant. The novel c.601A>G: p.Lys201Glu variant shows a mother-daughter transmission pattern across four generations. The proband exhibits focal epilepsy and achieved seizure freedom with a combination of oxcarbazepine and levetiracetam. All other affected members have no history of epileptic seizures. Brain MRIs of the affected members shows predominant fronto-central SBH with mixed pachygyria on the overlying cortex. The two nonsense variants were identified in two unrelated probands with SBH, severe drug-resistant epilepsy and intellectual disability. These novel DCX variants further expand the genotypic-phenotypic correlations of lissencephaly spectrum disorders. Our documented phenotypic descriptions of three unrelated families provide valuable insights and stimulate further discussions on DCX-SBH cases.

Morphological Signatures of Neurogenesis and Neuronal Migration in Hypothalamic Vasopressinergic Magnocellular Nuclei of the Adult Rat.

The arginine vasopressin (AVP)-magnocellular neurosecretory system (AVPMNS) in the hypothalamus plays a critical role in homeostatic regulation as well as in allostatic motivational behaviors. However, it remains unclear whether adult neurogenesis exists in the AVPMNS. By using immunoreaction against AVP, neurophysin II, glial fibrillar acidic protein (GFAP), cell division marker (Ki67), migrating neuroblast markers (doublecortin, DCX), microglial marker (Ionized calcium binding adaptor molecule 1, Iba1), and 5'-bromo-2'-deoxyuridine (BrdU), we report morphological evidence that low-rate neurogenesis and migration occur in adult AVPMNS in the rat hypothalamus. Tangential AVP/GFAP migration routes and AVP/DCX neuronal chains as well as ascending AVP axonal scaffolds were observed. Chronic water deprivation significantly increased the BrdU+ nuclei within both the supraaoptic (SON) and paraventricular (PVN) nuclei. These findings raise new questions about AVPMNS's potential hormonal role for brain physiological adaptation across the lifespan, with possible involvement in coping with homeostatic adversities.

Involvement of brain-derived neurotrophic factor methylation in the prefrontal cortex and hippocampus induced by chronic unpredictable mild stress in male mice.

Early life stress alters brain-derived neurotrophic factor (BDNF) promoter IV methylation and BDNF expression, which is closely related to the pathophysiological process of depression. However, the role of abnormal methylation of BDNF induced by stress during adolescence due to depression has not yet been clarified. In this study, adolescent mice were exposed to chronic unpredictable mild stress (CUMS). Depression-like behaviors, BDNF promoter IV methylation, expression of DNA methyltransferases (DNMTs), demethylation machinery enzymes, BDNF protein levels, and neuronal development in the prefrontal cortex (PFC) and hippocampus (HIP) were assessed in adolescent and adult mice. The DNMT inhibitor, 5-Aza-2-deoxycytidine (5-AzaD), was used as an intervention. Stress in adolescence induces behavioral dysfunction, elevated methylation levels of BDNF promoter IV, changes in the expression of DNMT, and demethylation machinery enzymes in adolescent and adult mice. Additionally, the stress in adolescence induced lower levels of BDNF and abnormal hippocampal doublecortin (DCX) expression in adolescent and adult mice. However, DNMT inhibitor treatment in adolescent-stressed mice relieved the abnormal behaviors, normalized the methylation level of BDNF promoter IV, BDNF protein expression, expression of DNMTs, and demethylation machinery enzymes, and improved the neuronal development of adult mice. These results suggest that stress in adolescence induces short- and long-term hypermethylation of BDNF promoter IV, which is regulated by DNMTs, and leads to the development of depression.

Semi-Synthesis of Different Pyranoflavonoid Backbones and the Neurogenic Potential.

Flavonoids and chalcones are known for their manifold biological activities, of which many affect the central nervous system. Pyranochalcones were recently shown to have a great neurogenic potential, which is partly due to a specific structural motif-the pyran ring. Accordingly, we questioned if other flavonoid backbones with a pyran ring as structural moiety would also show neurogenic potential. Different semi-synthetic approaches starting with the prenylated chalcone xanthohumol, isolated from hops, led to pyranoflavanoids with different backbones. We identified the chalcone backbone as the most active backbone with pyran ring using a reporter gene assay based on the promoter activity of doublecortin, an early neuronal marker. Pyranochalcones therefore appear to be promising compounds for further development as a treatment strategy for neurodegenerative diseases.

Novel lissencephaly-associated DCX variants in the C-terminal DCX domain affect microtubule binding and dynamics.

OBJECTIVE: Pathogenic variants in DCX on the X chromosome lead to lissencephaly and subcortical band heterotopia (SBH), brain malformations caused by neuronal migration defects. Its product doublecortin (DCX) binds to microtubules to modulate microtubule polymerization. How pathogenic DCX variants affect these activities remains not fully investigated. METHODS: DCX variants were identified using whole exome and Sanger sequencing from six families with lissencephaly/SBH. We examined how these variants affect DCX functions using microtubule binding, regrowth, and colocalization assays. RESULTS: We found novel DCX variants p.Val177AlafsTer31 and p.Gly188Trp, as well as reported variants p.Arg196His, p.Lys202Met, and p.Thr203Ala. Incidentally, all of the missense variants were clustered on the C-terminal DCX domain. The microtubule binding ability was significantly decreased in p.Val177AlafsTer31, p.Gly188Trp, p.Lys202Met, and previously reported p.Asp262Gly variants. Furthermore, expression of p.Val177AlafsTer31, p.Gly188Trp, p.Arg196His, p.Lys202Met, and p.Asp262Gly variants hindered microtubule growth in cells. There were also decreases in the colocalization of p.Val177AlafsTer31, p.Thr203Ala, and p.Asp262Gly variants to microtubules. SIGNIFICANCE: Our results indicate that these variants in the C-terminal DCX domain altered microtubule binding and dynamics, which may underlie neuronal migration defects during brain development.

Connecting DCX, COMT and FMR1 in social behavior and cognitive impairment.

Genetic variants of DCX, COMT and FMR1 have been linked to neurodevelopmental disorders related to intellectual disability and social behavior. In this systematic review we examine the roles of the DCX, COMT and FMR1 genes in the context of hippocampal neurogenesis with respect to these disorders with the aim of identifying important hubs and signaling pathways that may bridge these conditions. Taken together our findings indicate that factors connecting DCX, COMT, and FMR1 in intellectual disability and social behavior may converge at Wnt signaling, neuron migration, and axon and dendrite morphogenesis. Data derived from genomic research has identified a multitude of genes that are linked to brain disorders and developmental differences. Information about where and how these genes function and cooperate is lagging behind. The approach used here may help to shed light on the biological underpinnings in which key genes interface and may prove useful for the testing of specific hypotheses.

Pseudo-repeats in doublecortin make distinct mechanistic contributions to microtubule regulation.

Doublecortin (DCX) is a neuronal microtubule-associated protein (MAP) indispensable for brain development. Its flexibly linked doublecortin (DC) domains-NDC and CDC-mediate microtubule (MT) nucleation and stabilization, but it is unclear how. Using high-resolution time-resolved cryo-EM, we mapped NDC and CDC interactions with tubulin at different MT polymerization stages and studied their functional effects on MT dynamics using TIRF microscopy. Although coupled, each DC repeat within DCX appears to have a distinct role in MT nucleation and stabilization: CDC is a conformationally plastic module that appears to facilitate MT nucleation and stabilize tubulin-tubulin contacts in the nascent MT lattice, while NDC appears to be favored along the mature lattice, providing MT stabilization. Our structures of MT-bound DC domains also explain in unprecedented detail the DCX mutation-related brain defects observed in the clinic. This modular composition of DCX reflects a common design principle among MAPs where pseudo-repeats of tubulin/MT binding elements chaperone or stabilize distinct conformational transitions to regulate distinct stages of MT dynamic instability.

Human cytomegalovirus infection is associated with increased expression of the lissencephaly gene PAFAH1B1 encoding LIS1 in neural stem cells and congenitally infected brains.

Congenital infection of the central nervous system by human cytomegalovirus (HCMV) is a leading cause of permanent sequelae, including mental retardation or neurodevelopmental abnormalities. The most severe complications include smooth brain or polymicrogyria, which are both indicative of abnormal migration of neural cells, although the underlying mechanisms remain to be determined. To gain better insight on the pathogenesis of such sequelae, we assessed the expression levels of a set of neurogenesis-related genes, using HCMV-infected human neural stem cells derived from embryonic stem cells (NSCs). Among the 84 genes tested, we found dramatically increased expression of the gene PAFAH1B1, encoding LIS1 (lissencephaly-1), in HCMV-infected versus uninfected NSCs. Consistent with these findings, western blotting and immunofluorescence analyses confirmed the increased levels of LIS1 in HCMV-infected NSCs at the protein level. We next assessed the migratory abilities of HCMV-infected NSCs and observed that infection strongly impaired the migration of NSCs, without detectable effect on their proliferation. Moreover, we observed increased immunostaining for LIS1 in brains of congenitally infected fetuses, but not in control samples, highlighting the clinical relevance of our findings. Of note, PAFAH1B1 mutations (resulting in either haploinsufficiency or gain of function) are primary causes of hereditary neurodevelopmental diseases. Notably, mutations resulting in PAFAH1B1 haploinsufficiency cause classic lissencephaly. Taken together, our findings suggest that PAFAH1B1 is a critical target of HCMV infection. They also shine a new light on the pathophysiological basis of the neurological outcomes of congenital HCMV infection, by suggesting that defective neural cell migration might contribute to the pathogenesis of the neurodevelopmental sequelae of infection. © 2021 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Nestin Selectively Facilitates the Phosphorylation of the Lissencephaly-Linked Protein Doublecortin (DCX) by cdk5/p35 to Regulate Growth Cone Morphology and Sema3a Sensitivity in Developing Neurons.

Nestin, an intermediate filament protein widely used as a marker of neural progenitors, was recently found to be expressed transiently in developing cortical neurons in culture and in developing mouse cortex. In young cortical cultures, nestin regulates axonal growth cone morphology. In addition, nestin, which is known to bind the neuronal cdk5/p35 kinase, affects responses to axon guidance cues upstream of cdk5, specifically, to Sema3a. Changes in growth cone morphology require rearrangements of cytoskeletal networks, and changes in microtubules and actin filaments are well studied. In contrast, the roles of intermediate filament proteins in this process are poorly understood, even in cultured neurons. Here, we investigate the molecular mechanism by which nestin affects growth cone morphology and Sema3a sensitivity. We find that nestin selectively facilitates the phosphorylation of the lissencephaly-linked protein doublecortin (DCX) by cdk5/p35, but the phosphorylation of other cdk5 substrates is not affected by nestin. We uncover that this substrate selectivity is based on the ability of nestin to interact with DCX, but not with other cdk5 substrates. Nestin thus creates a selective scaffold for DCX with activated cdk5/p35. Last, we use cortical cultures derived from Dcx KO mice to show that the effects of nestin on growth cone morphology and on Sema3a sensitivity are DCX-dependent, thus suggesting a functional role for the DCX-nestin complex in neurons. We propose that nestin changes growth cone behavior by regulating the intracellular kinase signaling environment in developing neurons. The sex of animal subjects is unknown.SIGNIFICANCE STATEMENT Nestin, an intermediate filament protein highly expressed in neural progenitors, was recently identified in developing neurons where it regulates growth cone morphology and responsiveness to the guidance cue Sema3a. Changes in growth cone morphology require rearrangements of cytoskeletal networks, but the roles of intermediate filaments in this process are poorly understood. We now report that nestin selectively facilitates phosphorylation of the lissencephaly-linked doublecortin (DCX) by cdk5/p35, but the phosphorylation of other cdk5 substrates is not affected. This substrate selectivity is based on preferential scaffolding of DCX, cdk5, and p35 by nestin. Additionally, we demonstrate a functional role for the DCX-nestin complex in neurons. We propose that nestin changes growth cone behavior by regulating intracellular kinase signaling in developing neurons.

Hypothalamic plasticity in response to changes in photoperiod and food quality: An adaptation to support pre-migratory fattening in songbirds?

In latitudinal avian migrants, increasing photoperiods induce fat deposition and body mass increase, and subsequent night-time migratory restlessness in captive birds, but the underlying mechanisms remain poorly understood. We hypothesized that an enhanced hypothalamic neuronal plasticity was associated with the photostimulated spring migration phenotype. We tested this idea in adult migratory red-headed buntings (Emberiza bruniceps), as compared with resident Indian weaverbirds (Ploceus philippinus). Birds were exposed to a stimulatory long photoperiod (14L:10D, LP), while controls were kept on a short photoperiod (10L:14D, SP). Under both photoperiods, one half of birds also received a high calorie, protein- and fat-rich diet (SP-R, LP-R) while the other half stayed on the normal diet (SP-N, LP-N). Thirty days later, as expected, the LP had induced multiple changes in the behaviour and physiology in migratory buntings. Photostimulated buntings also developed a preference for the rich food diet. Most interestingly, the LP and the rich diet, both separately and in association, increased neurogenesis in the mediobasal hypothalamus (MBH), as measured by an increased number of cells immunoreactive for doublecortin (DCX), a marker of recently born neurons, in buntings, but not weaverbirds. This neurogenesis was associated with an increased density of fibres immunoreactive for the orexigenic neuropeptide Y (NPY). This hypothalamic plasticity observed in a migratory, but not in a non-migratory, species in response to photoperiod and food quality might represent an adaptation to the pre-migratory fattening, as required to support the extensive energy expenses that incur during the migratory flight.

Olig2 regulates terminal differentiation and maturation of peripheral olfactory sensory neurons.

The bHLH transcription factor Olig2 is required for sequential cell fate determination of both motor neurons and oligodendrocytes and for progenitor proliferation in the central nervous system. However, the role of Olig2 in peripheral sensory neurogenesis remains unknown. We report that Olig2 is transiently expressed in the newly differentiated olfactory sensory neurons (OSNs) and is down-regulated in the mature OSNs in mice from early gestation to adulthood. Genetic fate mapping demonstrates that Olig2-expressing cells solely give rise to OSNs in the peripheral olfactory system. Olig2 depletion does not affect the proliferation of peripheral olfactory progenitors and the fate determination of OSNs, sustentacular cells, and the olfactory ensheathing cells. However, the terminal differentiation and maturation of OSNs are compromised in either Olig2 single or Olig1/Olig2 double knockout mice, associated with significantly diminished expression of multiple OSN maturation and odorant signaling genes, including Omp, Gnal, Adcy3, and Olfr15. We further demonstrate that Olig2 binds to the E-box in the Omp promoter region to regulate its expression. Taken together, our results reveal a distinctly novel function of Olig2 in the periphery nervous system to regulate the terminal differentiation and maturation of olfactory sensory neurons.

Dual Mkk4 and Mkk7 Gene Deletion in Adult Mouse Causes an Impairment of Hippocampal Immature Granule Cells.

(1) Background: The c-Jun-NH2-terminal protein kinase (JNK) is a mitogen-activated protein kinase involved in regulating physiological processes in the central nervous system. However, the dual genetic deletion of Mkk4 and Mkk7 (upstream activators of JNK) in adult mice is not reported. The aim of this study was to induce the genetic deletion of Mkk4/Mkk7 in adult mice and analyze their effect in hippocampal neurogenesis. (2) Methods: To achieve this goal, Actin-CreERT2 (Cre+/-), Mkk4flox/flox, Mkk7flox/flox mice were created. The administration of tamoxifen in these 2-month-old mice induced the gene deletion (Actin-CreERT2 (Cre+/-), Mkk4∆/∆, Mkk7∆/∆ genotype), which was verified by PCR, Western blot, and immunohistochemistry techniques. (3) Results: The levels of MKK4/MKK7 at 7 and 14 days after tamoxifen administration were not eliminated totally in CNS, unlike what happens in the liver and heart. These data could be correlated with the high levels of these proteins in CNS. In the hippocampus, the deletion of Mkk4/Mkk7 induced a misalignment position of immature hippocampal neurons together with alterations in their dendritic architecture pattern and maturation process jointly to the diminution of JNK phosphorylation. (4) Conclusion: All these data supported that the MKK4/MKK7-JNK pathway has a role in adult neurogenic activity.

Profiling Glioblastoma Cases with an Expression of DCX, OLIG2 and NES.

Glioblastoma (GBM) remains the leading cause of cancer-related deaths with the lowest five-year survival rates among all of the human cancers. Multiple factors contribute to its poor outcome, including intratumor heterogeneity, along with migratory and invasive capacities of tumour cells. Over the last several years Doublecortin (DCX) has been one of the debatable factors influencing GBM cells' migration. To resolve DCX's ambiguous role in GBM cells' migration, we set to analyse the expression patterns of DCX along with Nestin (NES) and Oligodendrocyte lineage transcription factor 2 (OLIG2) in 17 cases of GBM, using immunohistochemistry, followed by an analysis of single-cell RNA-seq data. Our results showed that only a small subset of DCX positive (DCX+) cells was present in the tumour. Moreover, no particular pattern emerged when analysing DCX+ cells relative position to the tumour margin. By looking into single-cell RNA-seq data, the majority of DCX+ cells were classified as non-cancerous, with a small subset of cells that could be regarded as glioma stem cells. In conclusion, our findings support the notion that glioma cells express DCX; however, there is no clear evidence to prove that DCX participates in GBM cell migration.

Doublecortin undergo nucleocytoplasmic transport via the RanGTPase signaling to promote glioma progression.

BACKGROUND: Nuclear translocation of several oncogenic proteins have previously been reported, but neither the translocation of doublecortin (DCX) nor the mechanism involved has been studied. DCX is a neuronal microtubule-associated protein (MAP) that is crucial for adult neurogenesis and neuronal migration and has been associated with poor prognosis in gliomas. METHODS: We probed DCX expression in different grades of glioma tissues and conventional cells via western blotting. Then we analyzed the expression pattern in the Oncomine cancer profiling database. Confocal Immunofluorescence was used to detect DCX expression in the cellular compartments, while subcellular fractionation was probed via western blotting. Pulse shape height analysis was utilized to verify DCX localization in a larger population of cells. Co-immunoprecipitation was used in detecting DCX-import receptors interactions. To probe for DCX functions, stable cells expressing high DCX expression or knockdown were generated using CRISPR-Cas9 viral transfection, while plasmid site-directed mutant constructs were used to validate putative nuclear localization sequence (NLS) predicted via conventional algorithms and comparison with classical NLSs. in-silico modeling was performed to validate DCX interactions with import receptors via the selected putative NLS. Effects of DCX high expression, knockdown, mutation, and/or deletion of putative NLS sites were probed via Boyden's invasion assay and wound healing migration assays, and viability was detected by CCK8 assays in-vitro, while xenograft tumor model was performed in nude mice. RESULTS: DCX undergoes nucleocytoplasmic movement via the RanGTPase signaling pathway with an NLS located on the N-terminus between serine47-tyrosine70. This translocation could be stimulated by MARK's phosphorylation of the serine 47 residue flanking the NLS due to aberrant expression of glial cell line-derived neurotrophic factor (GDNF). High expression and nuclear accumulation of DCX improve invasive glioma abilities in-vitro and in-vivo. Moreover, knocking down or blocking DCX nuclear import attenuates invasiveness and proliferation of glioma cells. CONCLUSION: Collectively, this study highlights a remarkable phenomenon in glioma, hence revealing potential glioma dependencies on DCX expression, which is amenable to targeted therapy. Video abstract.

Recent advances in one-stage conversion of lipid-based biomass-derived oils into fuel components - aromatics and isomerized alkanes.

Nowadays, production of biofuels is a rather hot topic due to depleting of conventional fossil fuel feedstocks and a number of other factors. Plant lipid-based feedstocks are very important for production of diesel-, kerosene-, and gasoline-like hydrocarbons. Usually, (hydro)deoxygenation processes are aimed at obtaining of linear hydrocarbons known to have poor fuel characteristics compared to the branched ones. Thus, further hydroisomerization is required to improve their properties as motor fuel components. This review article is focused on conversion of lipid-based feedstocks and model compounds into high-quality fuel components for a single step - direct cracking into aromatics and merged hydrodeoxygenation-hydroisomerization to obtain isoparaffins. The second process is quite novel and a number of the research articles presented in the literature is relatively low. As auxiliary subsections, hydroisomerization of straight hydrocarbons and techno-economic analysis of renewable diesel-like fuel production are briefly reviewed as well.

A dominant dendrite phenotype caused by the disease-associated G253D mutation in doublecortin (DCX) is not due to its endocytosis defect.

Doublecortin (DCX) is a protein needed for cortical development, and DCX mutations cause cortical malformations in humans. The microtubule-binding activity of DCX is well-described and is important for its function, such as supporting neuronal migration and dendrite growth during development. Previous work showed that microtubule binding is not sufficient for DCX-mediated promotion of dendrite growth and that domains in DCX's C terminus are also required. The more C-terminal regions of DCX bind several other proteins, including the adhesion receptor neurofascin and clathrin adaptors. We recently identified a role for DCX in endocytosis of neurofascin. The disease-associated DCX-G253D mutant protein is known to be deficient in binding neurofascin, and we now asked if disruption of neurofascin endocytosis underlies the DCX-G253D-associated pathology. We first demonstrated that DCX functions in endocytosis as a complex with both the clathrin adaptor AP-2 and neurofascin: disrupting either clathrin adaptor binding (DCX-ALPA) or neurofascin binding (DCX-G253D) decreased neurofascin endocytosis in primary neurons. We then investigated a known function for DCX, namely, increasing dendrite growth in cultured neurons. Surprisingly, we found that the DCX-ALPA and DCX-G253D mutants yield distinct dendrite phenotypes. Unlike DCX-ALPA, DCX-G253D caused a dominant-negative dendrite growth phenotype. The endocytosis defect of DCX-G253D thus was separable from its detrimental effects on dendrite growth. We recently identified Dcx-R59H as a dominant allele and can now classify Dcx-G253D as a second Dcx allele that acts dominantly to cause pathology, but does so via a different mechanism.

Hippocampal Neurogenesis in Conditions of Chronic Stress Induced by Sciatic Nerve Injury in the Rat.

The dentate gyrus of the hippocampus is the primary location of adult neurogenesis, which is affected by a variety of external and internal factors, including activity of surrounding glial cells. This study concerns alterations in hippocampal neurogenesis and changes in activity of both proinflammatory and neuroprotective microglia/macrophages after sciatic nerve injury in the rat. Here, we demonstrated that the chronic pain induced by a peripheral nerve injury manifests in the hippocampus by a decrease in proliferation (PCNA+) and neurogenesis (DCX+), an increase in proinflammatory cytokines (CD86+), and a reduction in neuroprotective (CD163+) microglia/macrophages. We suggest that a pathological increase microglia/macrophage activity is the cause of neurogenesis suppression observed in chronic neuropathic pain.

Stable Adult Hippocampal Neurogenesis in Cannabinoid Receptor CB2 Deficient Mice.

The G-protein coupled cannabinoid receptor 2 (CB2) has been implicated in the regulation of adult neurogenesis in the hippocampus. The contribution of CB2 towards basal levels of proliferation and the number of neural progenitors in the subgranular zone (SGZ) of the dentate gyrus, however, remain unclear. We stained hippocampal brain sections of 16- to 17-week-old wildtype and CB2-deficient mice, for neural progenitor and immature neuron markers doublecortin (DCX) and calretinin (CR) and for the proliferation marker Ki67 and quantified the number of positive cells in the SGZ. The quantification revealed that CB2 deficiency neither altered overall cell proliferation nor the size of the DCX+ or DCX and CR double-positive populations in the SGZ compared to control animals. The results indicate that CB2 might not contribute to basal levels of adult neurogenesis in four-month-old healthy mice. CB2 signaling might be more relevant in conditions where adult neurogenesis is dynamically regulated, such as neuroinflammation.

Constant light environment suppresses maturation and reduces complexity of new born neuron processes in the hippocampus and caudal nidopallium of a diurnal corvid: Implication for impairment of the learning and cognitive performance.

Periodic day-night environment shapes the temporal pattern in the behaviour and physiology (e.g. 24-h activity-rest and sleep-wake cycles) and the advanced brain function, such as learning, memory and decision making. In a previous study, we showed the abolition of 24-h rhythm in the activity-rest pattern, and an attenuated cognitive performance in diurnal Indian house crows (Corvus splendens) under constant light (no-night; LL) environment. Present study extended this, and investigated LL-induced effects on the neurogenesis (birth, maturation and neurite complexity of new born neurons) in the hippocampus and caudal nidopallium, the brain regions directly associated with learning and cognition in birds. We performed immunohistochemistry of doublecortin (DCX; a neurogenesis marker) and tyrosine hydroxylase (TH, a key enzyme of the dopamine biosynthesis) in the brain section containing hippocampus or caudal nidopallium of Indian house crows exposed for 2 weeks to LL, with controls maintained under 12L:12D. As expected, crows showed arrhythmicity with a significantly reduced rest period in the 24-h activity-rest pattern, and a decreased cognitive performance when tested for the spatial and pattern association learning tasks under LL. Importantly, there was a significant decrease in DCX-immunoreactive (ir) cells and, as shown by Sholl analysis, in the complexity of DCX-ir neurites in both, the hippocampus and caudal nidopallium of crows under LL, as compared to those under 12L:12D. The anatomical proximity of DCX-ir neurons with TH-ir fibers suggested a functional association of the new born hippocampal and caudal nidopallial neurons with the learning, and perhaps cognition in Indian house crows. These results give insights into possible impact of the loss of night on brain health and functions in an emerging ecosystem in which other diurnal species including humans may be inadvertently exposed to an illuminated night, such as in an overly lighted metropolitan urban habitat.

ADAM10-Initiated Release of Notch Intracellular Domain Regulates Microtubule Stability and Radial Migration of Cortical Neurons.

Proper neuronal migration is orchestrated by combined membrane signal paradigms, whereas the role and mechanism of regulated intramembrane proteolysis (RIP) remain to be illustrated. We show here that the disintegrin and metalloprotease-domain containing protein 10 (ADAM10) regulates cortical neurons migration by initiating the RIP of Notch. We found that Notch intracellular domain (NICD) significantly rescued the migration defect of ADAM10-deficient neurons. Moreover, ADAM10 deficiency led to reduced neuronal motility and disrupted microtubule (MT) structure, which were associated with downregulated expression of acetylated tubulin and MT-associated proteins. Specifically, the NICD/RBPJ complex bound directly to the promoter, and regulated the neuronal expression level of doublecortin (DCX), a modulator of the MT cytoskeleton. Functionally, DCX overexpression largely restored neuron motility and reversed migration defect caused by ADAM10 knockout. Taken together, these findings demonstrate the direct requirement of ADAM10 in cortical radial migration and reveal the underlying mechanism by linking ADAM10-initiated RIP of Notch to the regulation of MT cytoskeleton through transcriptional control of Dcx expression.